You might want to trade it in for a diesel if you need to stick to the same size truck. My parents have a 454 gas Chevy for towing the camper 5-6mpg towing. My other buddy has a ford turbo diesel for towing his race car 15-17mpg towing. granted the diesel has a smell you would have to get used to but at least you would be tripling you mpg.
Why veasna drives a Suburban really shouldn't matter - maximizing it's FE potential is the Q . Some very good basic starting points have been offered . Mods/swaps may not be viable due to loan/warranty/other finances - getting the most out of what ya got is the name of the game .
Welcome to Gassavers veasna !